Import normals doesn't work
It seems like importing normals is impossible with 2.67 version of Blender. Blender recalculates them manually.

But for version 2.74 you can import custom normals using code sample:

normals2 = []
for l in mesh.loops:
    normals2.append(nlist[l.vertex_index])
mesh.normals_split_custom_set(normals2)
mesh.use_auto_smooth = True